Hitherto, various techniques for utilizing silver halide grains with a high silver chloride content (specifically, the silver halide grains having a chloride content of at least 95 mole %, which are referred to as the high-silver chloride grains hereinafter) have been proposed with the intention of making the photographic processing simple and rapid. Utilizing high-silver chloride grains has advantages of enhancing the reusability of processing solutions as well as increasing the development speed. Therefore, the photosensitive materials comprising high-silver chloride grains occupy the mainstream of photosensitive materials for printing, such as color photographic printing paper. In the present invention, processing time means the time from the initiation of processing (contact of a photographic material with a developing solution) to drying (Dry to Dry).
The high-silver chloride grains formed under ordinary conditions are grains having (100) faces as their external surfaces (referred to as {100} grains hereinafter). The grains put into practical use were also cubic grains. In recent years, tabular {100} grains have been developed since they have advantages of enabling effective spectral sensitization and ensuring a great covering power after development due to their large specific surface area (high ratio of the surface areas to the volume of each grain). Examples of such tabular grains are disclosed in U.S. Pat. Nos. 5,320,938, 5,264,337 and 5,292,632. Having high spectral sensitization efficiency is important particularly for high-silver chloride grains in which absorption of light in the blue-sensitive region is slight as compared with silver from iodide grains.
However, the high-silver chloride {100} grains have a problem of being easily fogged, as compared with commonly used silver bromide grains. In order to overcome this problem, high-silver chloride grains having (111) faces as their external surfaces (referred to as {111} grains) are utilized. Examples of these grains are disclosed in JP-A-6-138619 (the term "JP-A" as used herein means an "unexamined published Japanese patent application").
The formation of high-silver chloride {111} grains requires special contrivances. For instance, the method of forming high-silver chloride tabular grains in the presence of ammonia is disclosed by Wey in U.S. Pat. No. 4,399,215. The use of ammonia makes it difficult to form practically useful fine grains because silver chloride grains originally having high solubility is produced with a higher solubility condition. In addition, the pH at the time of manufacturing grain is raised to 8-10 by the use of ammonia; as a result, the grains are easily fogged. On the other hand, the high-silver chloride {111} grains formed in the presence of thiocyanates are disclosed by Maskasky in U.S. Pat. No. 5,061,617. Similarly to ammonia, the thiocyanates increase the solubility of silver chloride.
Further, there are known the methods of using the following additives [crystal phase controlling agents (which is sometimes called crystal habit control agents)] at the time of grain formation for the purpose of forming high-chloride grains the surfaces of which are constituted of (111) faces:
Crystal habit Document control agent Inventor U.S. Pat. No. 4,400,463 Azaindenes + Maskasky Thioether peptizer U.S. Pat. No. 4,783,398 2,4-Dithiazolidinone Mifune et al. U.S. Pat. No. 4,713,323 Aminopyrazolopyrimi- Maskasky dine U.S. Pat. No. 4,983,508 Bispyrimidinium salts Ishiguro et al. U.S. Pat. No. 5,185,239 Triaminopyridine Maskasky U.S. Pat. No. 5,178,997 7-Azaindole compounds Maskasky U.S. Pat. No. 5,178,998 Xanthine Maskasky JP-A-64-70741 Dyes Nishikawa et al. JP-A-3-212639 Aminothioether Ishiguro JP-A-4-283742 Thiourea derivatives Ishiguro JP-A-4-335632 Triazolium salts Ishiguro JP-A-2-32 Bispyridinium salts Ishiguro et al. JP-A-8-227117 Monopyridinium salts Ozeki et al.
The grains obtained using those methods have comparatively large sizes, specifically an average equivalent circle diameter of about 1 .mu.m (the term "average equivalent circle diameter" used herein means the average value of diameters of circles having the same areas as the projected areas of grains). From a practical point of view, however, it has so far been desired to form silver halide grains having a thin tabular shape, a high silver chloride content and grain sizes smaller than those achievable by the methods described above. In particular, thin tabular grains have been desired because they have a large specific surface area. Examples of thin high-silver chloride {111} tabular grains are disclosed in U.S. Pat. Nos. 5,217,858 and 5,183,732. However, a decrease in thickness of tabular grains causes a problem that the grains are easily dissolved during the photographic processing. In the practical color development-processing, the photosensitive materials are passed through a developer, a bleach-fixing solution and a washing solution in this order. Therefore, there is great danger of contaminating a developer with a fix-bleaching solution. As a result of the contamination, dissolution physical development impairs the photographic properties (sensitizing and increasing contrast). These phenomena are also promoted by decrease in grain size.
When the grain thickness distribution or/and the grain size distribution are broad (polydispersed), the grains in a thin grain section or a small size section of the distribution are especially subject to dissolution, and so they have low stability in processing solutions. In the documents described above, the tabular grains having an average equivalent circle diameter of 0.8 .mu.m or less are disclosed, but the proportion of such tabular grains to the total grains is 85%, on a projected area basis. In the case of containing iodide in tabular grains, the proportion of the tabular grains to the total grains is 70%. When the grains having different grain shapes are intermingled, they lack the uniformity in adsorption of sensitizing dyes thereto and the chemical sensitization thereof to result in deterioration of photographic characteristics.